The electron guns for cathode ray tubes that use an oxide cathode are geared towards low cost, “low consumption” systems, this low consumption resulting from new designs of the parts that make up the gun or from the part assembly techniques. The reduction in power, which, according to the state of the art, is normally approximately 4.5 W for the three cathodes, to values approximating 2.1 W, entails introducing more compact and thermally optimized systems. The use of small filament and cathode are essential to achieving the low powers required but are still inadequate. To reduce said consumption, the thermal losses must be reduced while keeping the systems simple to avoid any cost overhead compared to the standard system.
A number of techniques have been explored to reduce the thermal losses of the filament cathode structure.
The first solution involves facilitating the thermal transfer between the filament and the cathode, for example by modifying the internal absorptivity of the skirt of the cathode sleeve.
To facilitate the thermal transfer between the filament and the cathode, the interior of the skirt of the cathode is blackened by deposition or treatment to promote the absorption of the heat by the skirt, the radiative transfer between the two entities then being more effective. This method is, for example, described in the U.S. Pat. No. 5,543,682.
This solution is effective in facilitating the filament-cathode transfer but requires a relatively complicated production process, such as vapour deposition and its application is therefore costly.
A second solution, as described in U.S. Pat. No. 4,558,254, consists in modifying the shape of the skirt of the cathode sleeve itself, by giving it an S-shape combined with reducing the thickness in this area, in order to augment the conduction path and reduce the passage section of the conductive flow between the hot zone of the cathode and its support.
Another solution proposed by the latter US patent consists in limiting the thermal losses by radiation towards the rear of the cathode using a long cathode with several diameters.
All these solutions are difficult to implement and are costly for producing cathode ray tubes particularly suited to television.